Row Level Security in Power BI Report Server

I think what you want is to have a slicer that shows only the sales territories that the logged-in user is allowed to see, that you want to do that by showing the sales territory in the slicer and filtering the slicer using the filterRLS measure.  Problem is that you can't put a visual filter on a slicer.

There may be some kind of hack or workaround, but not one I'm aware of off hand.  Best I can think of is instead of a slicer, having a table that lists all the sales territories and when the user clicks on a row in that table it filters everything else on the page.